Lead Recovery from Solid Residues of Copper Industry Using Triethylenetetramine Solution

minerals Article Lead Recovery from Solid Residues of Copper Industry Using Triethylenetetramine Solution Mateusz Ciszewski * , Andrzej Chmielarz, Zbigniew Szołomicki, Michał Drzazga and Katarzyna Leszczy ńska-Sejda ŁUKASIEWICZ—Institute of Non-Ferrous Metals, Sowińskiego5, 44-100 Gliwice, Poland; [email protected] (A.C.); [email protected] (Z.S.); [email protected] (M.D.); [email protected] (K.L.-S.) * Correspondence: [email protected]; Tel.: +48-32-23-80-277 Abstract: Industrial processing of mineral ores and concentrates generates large amounts of solid residues, which can be landfilled or further processed to recover selected elements depending on its economical profitability. Pressure leaching is a technology enabling high recovery of base metals like copper and zinc, transferring others like lead and iron to the solid residue. High temperature and pressure of such leaching leads to formation of sparingly soluble lead jarosite (plumbojarosite). The load of lead landfilled as solid residues resulting from such operation is so big that its recovery is perspective and crucial for waste-limiting technologies. This paper is devoted to lead extraction from pressure leaching residues using triethylenetetramine solution and then its precipitation as a commercial lead carbonate. The highest obtained recovery of lead was 91.3%. Additionally, presented technology allows to manage and recycle amine solution and reuse solid products. Produced pure lead carbonate can be directly added to smelting, not increasing temperature within the furnace. Citation: Ciszewski, M.; Chmielarz, A.; Szołomicki, Z.; Drzazga, M.; Keywords: triethylenetetramine; lead extraction; recycling; lead carbonate Leszczyńska-Sejda,K. Lead Recovery from Solid Residues of Copper Industry Using Triethylenetetramine Solution. Minerals 2021, 11, 546. 1. Introduction https://doi.org/10.3390/min11050546 Increasing metal demands and decreasing economic grades of copper deposits lead to seeking alternative routes to pyrometallurgical copper processing [1]. Historically, Academic Editors: Zygmunt Sadowski and Agnieszka Pawlowska the pyrometallurgical processing of ores dominated the copper industry since the 1800s, however, since the 1990s, the increase share of hydroprocessing plants can be observed [2]. Received: 15 April 2021 The advantages of hydrometallurgical technique include high metal recovery, greater Accepted: 18 May 2021 tolerance towards impurities, flexibility, modularity, lower energy consumption, and lower Published: 20 May 2021 capital costs of launching and commissioning of plants, however, limitations like lower productivity and large amounts of generated effluents and residues have to be taken Publisher’s Note: MDPI stays neutral into account too. An increase in leaching efficiency can be obtained using more severe with regard to jurisdictional claims in process conditions i.e., high temperature and pressure. Pressure leaching is based on ◦ published maps and institutional affil- acidic dissolution of the sulfide matrix at high temperature (at least 190 C) and pressure iations. (20 bars total) [3]. Depending on the acidity and the oxygen amount, the various iron compounds may be produced, either hematite (T < 200 ◦C, low acidity, reaction 1), basic iron sulfate (160 ◦C < T < 200 ◦C, high acidity, reaction 2), or jarosites (high acidity and + + + 2+ presence of K , NH4 , Ag , Pb , reaction 3 and 4) [4,5]. Presence of the specific metal 2+ + + + + Copyright: © 2021 by the authors. cations (Pb , Na ,K , Rb , Ag etc.) within the metal ore or concentrate may results in Licensee MDPI, Basel, Switzerland. different jarosites formation. This article is an open access article distributed under the terms and Fe2(SO4)3 + 3H2O = Fe2O3 + 3H2SO4 (hematite) (1) conditions of the Creative Commons Attribution (CC BY) license (https:// Fe2(SO4)3 + 2H2O = Fe(OH)SO4 + 8H2SO4 (oxidation + hydrolysis) (2) creativecommons.org/licenses/by/ 3Fe2(SO4)3 + 14H2O = 2H3OFe3(SO4)2(OH)6 (hydronium jarosite) (3) 4.0/). Minerals 2021, 11, 546. https://doi.org/10.3390/min11050546 https://www.mdpi.com/journal/minerals Minerals 2021, 11, 546 2 of 7 3Fe2(SO4)3 + M2SO4 +12H2O = 2 MFe3(SO4)2(OH)6 + 6H2SO4 (4) + + + 2+ where M = Ag , NH4 ,K , 1/2Pb . Formation of jarosite and basic iron sulfates are aimed to immobilize and remove iron from the reaction system. However, these compounds make environmental and processing problems in the future as well, as they both pose difficulties in further recovery of silver from the leaching residues [6]. There have been made several attempts to decompose yet produced jarosites using sulfuric acid [7], hydrochloric acid with an addition of calcium chloride [8], ammonia [9], and sodium or calcium hydroxides [10,11]. Among them, sulfuric acid seems to be the most convenient regarding further metal treatment as it is less corrosive and troublesome (vapours) in comparison to ammonia or hydrochloride. Additionally, for the proposed technology using triethylenetetramine solution, there is no need to make a next unit operation for chloride removal as sulfate ions can be “recovered” in a gypsum production stage [12–14]. Lead from decomposed lead jarosite can be then extracted using various techniques, mostly used for lead-acid battery paste desulfurization. In fact, desulfurization of battery paste containing lead sulfate and lead oxides leads to metal lead recovery [15,16]. Several hydrometallurgical attempts can be distinguished in lead sulfate processing with the use of sodium hydroxide, sodium carbonate, ammonium acetate, and citric acid among the most popular [17]. Depending on the stoichiometry of lead sulfate to sodium carbonate, the reaction products can be lead carbonate (PbCO3), lead hydroxycarbonate (Pb3(CO3)2(OH)2), or sodium lead hydroxycarbonate (NaPb2(CO3)2OH) and other intermediates [18]. Desulfurization with sodium carbonate or more troublesome sodium hydroxide generally exceeds 99% [19]. In both cases, up to 10% excess of desulfur- izing agent has to be used. Another approach for spent lead acid battery processing uses ammonium acetate, however, it requires thermal pretreatment of lead paste to oxidize metal impurities (Ca, Fe, Sb, Ba) and then sulfuric acid to produce soluble metal sulfates [20]. Phase separation of as obtained material allows to leach lead sulfate with ammonium acetate. Efficient desulfurization can be done using a mixture of sodium citrate and citric acid, resulting in lead citrate and sodium sulfate [21]. Decomposition of lead oxides (PbO and PbO2) requires excess of citric acid and addition of hydrogen peroxide. The perspective method to recover metal constituents from various solid materials like sludges, fly ashes (coal fly ash, oil-fired fly ash, municipal wastes incineration fly ash), electronic wastes, spent catalysts, as well as low grade ores and secondary wastes, is bioleaching [22]. This approach used with a proper pretreatment (catalyst, ultrasound, grinding) allows to signif- icantly enhance metal extraction. Here, we reported a novel approach to extract lead from pressure leaching residue priorly treated with sulfuric acid solution. Triethylenetetramine solution was used to extract lead sulfate, which was then carbonated to produce pure lead carbonate. The biggest advantage of the proposed methodology is the possibility to recycle the extracting solution, minimizing chemical consumption and environmental impact [23]. 2. Materials and Methods Solid residues were obtained in pressure leaching of copper concentrates deliv- ered from three different European copper mines (localized in Serbia—SE, Poland—PL, Portugal—OR). The main host mineral for copper was covellite (SE), chalcopyrite and bor- nite (PL), and chalcopyrite (OR). Copper concentration in polymetallic concentrates varied from 1.7% (SE), through 5.2% (OR) to 13% (PL). Processes were carried out at 190–200 ◦C with an oxygen overpressure 5–7 bars in a reactor equipped with heating jacket, cooling coils, baffles, temperature and pressure measurement instruments, gas feed valves and controllers, and mechanic agitator. Produced solid residue was filtered, washed with water and dried. In the pre-treatment, as-obtained solid residues were mixed with 1 M sulfuric acid solution at temperature 90 ◦C to decompose lead jarosite and produce lead sulfate. Resulting sludge was filtered and washed with water to remove free acid (confirmed by a pH test) and then treated with 6% w/w triethylenetetramine solution in water. Ex- traction of lead sulfate with amine was carried out for 1 h at 60 ◦C with the solid:liquid ratio 0.2. As triethylenetetramine is a viscous liquid, an increased temperature (60 ◦C) Minerals 2021, 11, 546 3 of 7 was used to enhance wettability and to improve metal salt extraction. pH was monitored within the process. It dropped from 11.5 for the fresh water-amine solution to 10 after an hour. A longer time did not cause any significant pH change, which may be ascribed to the end of the extraction process. Phases were then separated on Buchner funnel and filter cake was rinsed with water to remove any occluded amine droplets rich in lead sulfate. Filtrates and washings were then mixed and carbonated using specially-designed teflon- lined flotation machine equipped with agitator, stator, and gas nozzles enabling to deliver gas to the bottom of the reaction vessel and uniformly distributed it in a whole volume to achieve its high dissolution. Purging of carbon dioxide through lead sulfate containing triethylenetetramine solution led to precipitation

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